1. Field of the Invention
This invention relates to encoding apparatus and to methods associated with such. More particularly, the invention relates to application of acoustic methods to encoding keyboards.
2. Description of the Prior Art
Encoding apparatus for use with many and varied types of equipment have long been known. Yet, there is a continued search for low cost, simple encoders having high reliability. Apparatus of that type based on detection of acoustic wave fronts and specifically applied to keyboards have been briefly disclosed in IBM Technical Disclosure Bulletins--e.g., Arosenius, Vol. 14, No. 10, March 1972, and Lisk Vol. 29, No. 1 June 1977--and specific approaches using long rods or "bars" are more fully disclosed in the above-mentioned copending applications and in British Pat. No. 1,386,070. The third of the copending applications (Ser. No. 246,820, referred to hereinafter as "prior application III", for brevity) discloses an improved technique which relies on the polarity of the wave fronts to discriminate between different key inputs when accumulations of tolerances cause overlap in the elapsed times obtained upon depression of the different keys.
While such acoustic keyboards are a considerable improvement over known art, problems have been encountered when considerations of mass production have been introduced--particularly in connection with transfer of the encoding/decoding logic to single chips of the solid state variety applicable, say, to electronically controlled typewriters. The amount of logic required by the prior art (even including the abovementioned copending application III) is such as to approach or exceed the upper limits on the size of such chips. Accordingly, there is need for an encoding apparatus of the acoustic wave type using structure and a logic approach which is less demanding in terms of chip surface area.